# مقالههای Akbari

**توجه:**محتویات این صفحه به صورت خودکار پردازش شده و مقالههای نویسندگانی با تشابه اسمی، همگی در بخش یکسان نمایش داده میشوند.

##### ۱NATURAL STREAMS UNSTEADY SEDIMENT MOTION PREDICTED BY COMPLETE FULLY COUPLED NON–LINEAR NUMERICAL SOLUTIONS

نویسنده(ها):
Akbari

اطلاعات انتشار:
هفتمین کنگره بین المللی مهندسی عمران،
سال ۱۳۸۵

تعداد صفحات:
۷

The aims and objectives of the present work are unsteady flow–sediment transport and flood prediction in the natural streams, analysis of exisiting problems involved within the natural real rivers situations imposed by man, and looking at the effects of flooding on flow–sediment characteristics change within a certain period of time and at different locations along the reach. This study is particulary dealing with merits and disadvantage of several numerical solution techniques applied to real rivers flow – sediment transport regimes at upstream and downstream of a dam (river–reservoir system). The basic physical principles of conservation of mass and moment are used to describe the flow–sediment transport and flooding flow. A new approach for governing sediment particle movement is adopted to establish the interaction between the highly non – linear unsteady flow–sediment motion including , rapidly varying flooding flow transporting different sediment particles. Since the resulting mathematical formulation is highly non–linear and complex, it is impractical , if not impossible , to solve them analytical. Therefore the governing equations for flow–sediment continuity, momentum. Equations were solved numerically. To see the importance of non–linear terms in the governing equations, a comparison was made between different solutions when they were solved in linear coupled or uncoupled , and or in the most complete non–linear and fully coupled or uncoupled forms. This means that two phase of flow and sediment movements may or may not be considered together at a time step, i.e., by ignoring certain terms, the sediment continuity equation may be uncoupled from the other governing flow and hydraulic equations. Algorithms were developed for linear or non–linear and coupled or uncoupled solutions. Solutions were also obtained with the grain sorthing \ armouring included or excluded.<\div>

##### ۲A New Method for Musical Noise Detection and Evaluation in the Noise Reduction SYstems

اطلاعات انتشار:
سال ۱۳۹۵

تعداد صفحات:
۶

Subjective listening tests lead lo the ntost reliable results in evaluating the speech quality; hov,ever, they are very costly and time consuming–

Thus an objective measure which can predict the perceived subjective quality speech would be very helpful In this paper a new method for detecting the wide–band musical noise in the acoustic signal is proposed. Musical noise is one of the major distortiorts introduced into the background noise when processed by a noise reduction system. In this paper also an objective measure is proposed which can determine the

amount of the musicalness of the residual noise. The performance of the proposed measure was verified using subjectite listening tests. istening tests shov the high correlation of lhe proposed measure u'ilh lhe perceived subjective quality ofthe background noise<\div>

Thus an objective measure which can predict the perceived subjective quality speech would be very helpful In this paper a new method for detecting the wide–band musical noise in the acoustic signal is proposed. Musical noise is one of the major distortiorts introduced into the background noise when processed by a noise reduction system. In this paper also an objective measure is proposed which can determine the

amount of the musicalness of the residual noise. The performance of the proposed measure was verified using subjectite listening tests. istening tests shov the high correlation of lhe proposed measure u'ilh lhe perceived subjective quality ofthe background noise<\div>

##### ۳COMPUTATIONAL FLOW SEPARATION CONTROL USING ELECTROMAGNETIC FIELDS

اطلاعات انتشار:
چهاردهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۵

تعداد صفحات:
۸

Flow separation control by electromagnetic field was studied for a flat plate at high angles of incidence. Lorentz force were used as the model for the electromagnetic field and incorporated within a compressible Navier–Stokes flow solver. The compressible solver is based on an implicit, high resolution, and Total Variation Diminishing (TVD) scheme. The computational results were qualitatively compared with experimental observations. For a range of incidence angles, the electromagnetic field has completely prohibited flow separation and enhanced lift coefficient. However, the overall drag coefficient has been slightly increased due to the increase in skin friction.<\div>

##### ۴INVESTIGATION OF WAVE PATTERNS AND RESISTANCE OF SHIPS IN SHALLOW WATER

اطلاعات انتشار:
پانزدهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۶

تعداد صفحات:
۵

Flow fields and wave patterns are computed in the far field of a ship moving steadily, using Michell’s thin–ship theory. Having the wave records in far field, the wave resistance and also total resistance of ships are computed. Computed ship resistances are compared with experimental esults in different depths in shallow water. The numerical simulation is performed in subcritical, critical and supercritical regimes for different depth Froude numbers. However for the accuracy of simulation the effect of eddy viscosity is then considered. This method can be applied for

conventional ships with great accuracy and reliability.<\div>

conventional ships with great accuracy and reliability.<\div>

##### ۵Effect of Flow Channel Dimensions on the Performance of a PEM Fuel Cell Using 3D Modeling

اطلاعات انتشار:
پانزدهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۶

تعداد صفحات:
۸

In this study a steady–state three–dimensional computational fluid dynamics (CFD) model of a proton exchange membrane fuel cell is developed and presented for a single cell. A complete set of conservation equations of mass, momentum, species, energy transport, and charge is considered with proper account of electrochemical kinetics based on Butler– Vollmer equation. The effect of interfacial contact resistance is also considered in this model. The numerical solution is based on a finite–volume method. In this investigation a CFD code was used as the core

solver for the transport equations, while mathematical models for the main physical and electrochemical phenomena were devised into the solver using userdeveloped subroutines. The results of this model will allow detailed study of interdependencies between fluid dynamics, fluid flow, contact resistance, and electrochemical reactions. Polarization curves are obtained for different conditions. Simulation results show the effect of flow channel dimensions on the cell performance. An optimum shoulder size is predicted to exist for the cell's optimum performance. A comparison between the polarization curves obtained from the current study and the corresponding available experimental data is presented and a reasonable agreement is obtained. Such CFD model can be used as a tool in the development and optimization of PEM fuelcells.<\div>

solver for the transport equations, while mathematical models for the main physical and electrochemical phenomena were devised into the solver using userdeveloped subroutines. The results of this model will allow detailed study of interdependencies between fluid dynamics, fluid flow, contact resistance, and electrochemical reactions. Polarization curves are obtained for different conditions. Simulation results show the effect of flow channel dimensions on the cell performance. An optimum shoulder size is predicted to exist for the cell's optimum performance. A comparison between the polarization curves obtained from the current study and the corresponding available experimental data is presented and a reasonable agreement is obtained. Such CFD model can be used as a tool in the development and optimization of PEM fuelcells.<\div>

##### ۶Comparison of drag characteristics of toxic self–polishing co–polymers and nontoxic silicone foul release coatings

اطلاعات انتشار:
دومین همایش تخصصی مهندسی محیط زیست،
سال ۱۳۸۷

تعداد صفحات:
۹

With the imminent ban on the application of coatings of toxic TBT self–polishing co–polymers in January 2003 and their eventual prohibition in 2008 so, the second and more novel approach to fouling control and consequently drag reduction force is to make the surface “non–stick”, and prevent fouling attachment without the use of biocides (silicone fouling release coatings). An experimental study has been carried out to evaluate the drag characteristics of different toxic self–polishing co–polymers and a nontoxic silicone foul release coating. Drag measurements have been performed on a smooth aluminum cylinder connected to a rotor device. Various coatings on cylinders were examined and differential length technique was also used to avoid the end effects during rotation. AFM studies revealed a lower surface roughness for silicone FR coating as compared to SPC coatings. Also, its surface texture is considerably different from SPC coatings.<\div>

##### ۷SEDIMENT SORTING AND BED CHANGES IN LARGE RIVERS

نویسنده(ها):
Akbari

اطلاعات انتشار:
چهارمین کنگره ملی مهندسی عمران،
سال ۱۳۸۷

تعداد صفحات:
۷

In natural streams the flow varies from time to time, cross–sectional geometry changes and bed material is not uniform. Therefore, in a realistic flow–sediment transport prediction model, it is necessary to incorporate unsteady, non–uniform flow computation components, a sediment transport equation and a grain sorting and armouring algorithm in order tomodel water –sediment movement satisfactorily. The non–linear coupled model incorporated with and without a grain sorting and armouring algorithm for uniform and graded sediments (NCM and NCMG models) were applied to real river data and some sediment routing examples werestudied. The relative merits of the models were also discussed. The Missouri river downstream of Garrison dam is selected as a case study to deal with the most serious problems involved within a natural river. Descriptions of thisriver, the data sets used, and the results of application of the NCM and NCMG models to flow and sediment routing arediscussed in the following sections.<\div>

##### ۸SENSITIVITY OF SEDIMENT PREDICTION TO SIZE GRADATION

نویسنده(ها):
Akbari

اطلاعات انتشار:
چهارمین کنگره ملی مهندسی عمران،
سال ۱۳۸۷

تعداد صفحات:
۸

Varied unsteady flow–sediment equations for a graded river bed contain a variety of unknown sediment characteristics, hydraulic, and geometric parameters. These parameters, together with input data comprising initial and boundary conditions, would be required to simulate flow–sediment variations. Sensitivity analysis and optimisation procedure involves determining these parameters by fitting the model to either field or simulated data. Prior to optimisation a sensitivity analysis of existing flow–sediment parameters was found useful in highlighting the role of each parameter and reduced the time and number of iterations in the solution process. In this paper an optimization technique is employed for finding best fitted value of some important parameters involved in graded sediment routing and bed armouring processes using Advanced non–linear coupled model (ANCMG). The particular case study used for this investigation is degradation, bed armouring and grain size distribution of bed material in a river bed downstream a dam. For a graded river bed, the effects of bed roughness, sediment parameters and thickness of the active layer on sediment sizes, and bed level changes were studied. A combined Gauss–Newton and modified Newton method [9] was employed to calculate the optimised parameters.<\div>

##### ۹A FLOODING PREDICTION IN NATURAL RIVERS BY NUMERICAL CHARACTERISTICS SOLUTION

اطلاعات انتشار:
چهارمین کنگره ملی مهندسی عمران،
سال ۱۳۸۷

تعداد صفحات:
۵

Flooding prediction in large rivers of compound sections is studied. The highly variable unsteady entry of water and sediment to a reach and changes in base level are amongst examples of natural events that induce changes in a river flow–sediment regime. Man–made troubles to nature such as construction of hydraulic structures and the implementation of river training techniques like bank stabilisation, channel realignment,

dike construction, and dredging are some examples of artificial causes and problems imposed to river sediment transport regime. Generally a study of movable bed sediment propagation can be approached mathematically from either an analytical or a numerical stand–point. Analytical solutions can be obtained for simplified cases because the three governing equations (continuity and hydrodynamic of flow–sediment

transport equations) describing unsteady open channel flow with a movable boundary are first order, nonlinear partial differential equations of the hyperbolic type. Analytical models may be adequate only for an initial rapid evaluation of degradation and aggradation. Most situations, and in particular for highly variable flooding flows however, do not lend themselves to simplified solutions and more complete numerical methods then need to be adopted. In this paper numerical method of characteristics was used for prediction of flow–sediment prediction in large rivers.<\div>

dike construction, and dredging are some examples of artificial causes and problems imposed to river sediment transport regime. Generally a study of movable bed sediment propagation can be approached mathematically from either an analytical or a numerical stand–point. Analytical solutions can be obtained for simplified cases because the three governing equations (continuity and hydrodynamic of flow–sediment

transport equations) describing unsteady open channel flow with a movable boundary are first order, nonlinear partial differential equations of the hyperbolic type. Analytical models may be adequate only for an initial rapid evaluation of degradation and aggradation. Most situations, and in particular for highly variable flooding flows however, do not lend themselves to simplified solutions and more complete numerical methods then need to be adopted. In this paper numerical method of characteristics was used for prediction of flow–sediment prediction in large rivers.<\div>

##### ۱۰Investigation Grain Geometry Effects on the Performance of SRMs

اطلاعات انتشار:
شانزدهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۷

تعداد صفحات:
۵

The internal flow dynamics of a solid propellant rocketmotor (SRM) is very complex. The performance of asolid rocket motor depends heavily on the flowcharacteristics, the chemical composition of the grain,the temperature distribution and the combustionproducts. In this study internal ballistics of some solidrocket motors (SRM) are numerically simulated. A CFD simulation of the flowfield within a solidpropellant rocket motor with slightly tapered grainhas been developed. Also in this study the effect of erosive burning is investigated. Governing equations ofaxisymmetric inviscid flow are solved using an explicitMacCormack finite difference technique in which thelocations of shock waves are captured by the solutionscheme<\div>

##### ۱۱Damping–ratio effects on VIV of a cylinder—A numerical investigation

اطلاعات انتشار:
شانزدهمین کنفرانس سالانه مهندسی مکانیک،
سال ۱۳۸۷

تعداد صفحات:
۸

In this paper we present numerical results of the dynamic response to fluid forcing on an elastically mounted rigid cylinder with low mass–damping, allowed to oscillate transverse to a free stream. A vortex method is implemented to solve the two–dimensional Navier–Stokes equation in terms of vorticity. The Reynolds number ranges from 90 to 160, a regime that is fully laminar. The main objective of this paper is to investigate the effect of damping ratio on the transverse vibrational behavior of the cylinder. Numerical results predict that a decrease in damping ratio will result in an increase in the oscillation amplitude, while it will cause an increase in the velocity range over which lock–in occurs. The changes are not linear with respect to variation in damping ratio.<\div>

##### ۱۲Heat Exchanger Network Area Targeting Considering Stream Passage through Shell or Tubes

اطلاعات انتشار:
پنجمین کنگره بین المللی مهندسی شیمی،
سال ۱۳۸۶

تعداد صفحات:
۱۳

An optimal heat recovery network requires optimum values of area and energy targets. Current heat exchanger network targeting methods do not consider the optimal passage of each stream through the shell or tubes side of the exchanger during the network cost estimation. They usually pre–set the passage of the streams through shell or tubes ahead of targeting [1]. However, considerations of appropriate passage

of streams through the shell or tubes side can considerably affect the network costestimation. This paper introduces a new area targeting procedure which utilizes the optimal passage of each stream in all enthalpy intervals. The procedure evaluates two possible options for each stream split pass through each exchanger in the spaghetti network. One option is the hot stream passing through the shell while cold stream

passes through tubes. The next option is that the hot strea m passes through tubes and cold stream passes through the shell side. Therefore, two different exchanger area requirements can be estimated. From these two configurations, the one with less area requirement leads to the lower network cost. During this optimization process, the optimal distribution of each stream pressure drop within enthalpy intervals is fully

utilized. The proposed targeting procedure is applied for a case study and comparison of the results with previous methods [1] shows reduction of around 18% in the network area. In another case study, the area–energy trade off has been performed using the new procedure and a reduction of 12.4% and 14.5% in minimum network area requirement and total annual cost was observed respectively. It is concluded that the new procedure can considerably alter the area–energy trade off.<\div>

of streams through the shell or tubes side can considerably affect the network costestimation. This paper introduces a new area targeting procedure which utilizes the optimal passage of each stream in all enthalpy intervals. The procedure evaluates two possible options for each stream split pass through each exchanger in the spaghetti network. One option is the hot stream passing through the shell while cold stream

passes through tubes. The next option is that the hot strea m passes through tubes and cold stream passes through the shell side. Therefore, two different exchanger area requirements can be estimated. From these two configurations, the one with less area requirement leads to the lower network cost. During this optimization process, the optimal distribution of each stream pressure drop within enthalpy intervals is fully

utilized. The proposed targeting procedure is applied for a case study and comparison of the results with previous methods [1] shows reduction of around 18% in the network area. In another case study, the area–energy trade off has been performed using the new procedure and a reduction of 12.4% and 14.5% in minimum network area requirement and total annual cost was observed respectively. It is concluded that the new procedure can considerably alter the area–energy trade off.<\div>

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